Comparition between two Dates to find out No of days beteen them

[11MCA0152]

I want to input two dates, i want to compare these things:-
1) The second date should be greater than the first date
2) I also want to find out the no of days between these two dates

3) How can I set the current date as default date for the first calendar

I am using CalendarExtenda rTool of AJAX toolkit,